1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a multi-domain LCD device which includes a valley formed by irradiating a laser beam, and a simplified method for manufacturing the same.
2. Discussion of the Related Art
The demand for various display devices has increased. Accordingly, various flat display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), an electroluminescent display (ELD), and a vacuum fluorescent display (VFD) have been developed.
Among the various flat display devices, the LCD devices are used most widely due to advantageous characteristics of a thin profile, a lightness in weight, and low power consumption. Thus, the LCD devices are a substitute for a Cathode Ray Tube (CRT). In addition to mobile type LCD devices such as a display for a notebook computer, LCD devices have been developed for computer monitors and televisions.
Despite various technical developments in the LCD technology, research in enhancing the picture quality of the LCD device has been in some respects lacking as compared to other features and advantages of the LCD device. Therefore, in order to use the LCD device as a general display, an LCD having a high quality picture, such as high resolution and high luminance with a large-sized screen while still maintaining lightness in weight, thinness, and low power consumption is needed.
Generally, an LCD device includes an LCD panel that displays images, and a driver that applies a driving signal to the LCD panel. Further, the LCD panel includes first and second glass substrates that are bonded to each other at a predetermined interval, and a liquid crystal layer formed between the first and second substrates.
In addition, the first glass substrate (TFT array substrate) includes a plurality of gate lines, a plurality of data lines, a plurality of pixel electrodes, and a plurality of thin film transistors. The plurality of gate lines are formed at fixed intervals in a first direction, and the plurality of data lines are formed at fixed intervals in a second direction perpendicular to the first direction to thereby define a plurality of pixel regions. Then, the plurality of pixel electrodes, which are arranged in a matrix-type configuration, are respectively formed in the pixel regions. Also, the plurality of thin film transistors are switched according to signals of the gate lines so as to transmit signals of the data lines to the respective pixel electrodes.
In addition, the second glass substrate (color filter substrate) includes a black matrix layer that excludes light from regions except the pixel regions of the first glass substrate, a color filter layer of R(red)/G(green)/B(blue) for displaying various colors, and a common electrode to represent the picture image.
Further, the LCD device is driven according to optical anisotropy and polarizability of the liquid crystal material. That is, liquid crystal molecules of the liquid crystal layer are aligned using directional characteristics, because the liquid crystal molecules have a long and thin shape. In this respect, an induced electric field is applied to the liquid crystal material to control the alignment direction of the liquid crystal molecules. That is, when the alignment direction of the liquid crystal molecules is controlled by the induced electric field, the light is polarized and changed by the optical anisotropy of the liquid crystal, thereby displaying a picture image.
Further, the alignment of the liquid crystal molecules depends on the dielectric anisotropy of the liquid crystal formed between the first and second glass substrates. For example, a Twisted Nematic TN mode corresponds to the dielectric anisotropy of the liquid crystal being the positive type. A Vertical Alignment VA mode corresponds to the dielectric anisotropy of the liquid crystal being the negative type.
Also, one pixel region of the LCD device may be divided into a plurality of domains, which is referred to as a multi-domain mode. A multi-domain LCD device is advantageous, because it has a good picture quality and wide viewing angle. Further, it is also possible to combine the multi-domain mode with a vertical alignment (VA) mode, which is referred to as a multi-domain vertical alignment MVA mode.
Hereinafter, a related art MVA mode LCD device will be explained with reference to FIGS. 1-4.
As shown in FIGS. 2 and 3, the related art MVA mode LCD device includes a lower substrate 1, an upper substrate 2, and a liquid crystal layer 3. As shown in FIG. 1, the lower substrate 1 includes a gate line 11, a data line 12, a thin film transistor, and a pixel electrode 13. In addition, the gate line 11 is formed perpendicular to the data line 12 to thereby define a unit pixel region. Then, the thin film transistor (not shown) is formed adjacent to a crossing portion of the gate and data lines 11 and 12. The pixel electrode 13 is formed in the unit pixel region, and includes one or more transmitting parts 14 positioned at fixed intervals.
As shown in FIGS. 2 and 3, the upper substrate 2 includes a black matrix layer (not shown), a color filter layer 6 of red(R)/green(G)/blue(B), and a common electrode 7. The black matrix layer is formed corresponding to other portions except the pixel region (gate and data lines), and the color filter layer 6 is formed corresponding to the pixel region. Then, the common electrode 7 is formed on an entire surface of the upper substrate 2 including the color filter layer 6.
Also, a valley 15 is formed in the upper substrate 2 at a portion between the transmitting parts 14 of the pixel electrode 13. As shown, the valley 15 is patterned in a surface of the color filter layer 6, and the common electrode 7 is formed on the color filter layer 6 including the valley 15. Thus, the common electrode 7 includes a predetermined step coverage of the color filter layer 6 due to the valley 15.
In addition, the related art MVA mode LCD device also includes an alignment layer 21 formed on facing surfaces of the lower and upper substrates 1 and 2, or on any one of the lower and upper substrates 1 and 2. Further, the alignment layer 21 is rubbed such that the alignment layer 21 has a vertical pretilt angle. In FIGS. 2 and 3, the alignment layer 21 is formed only on the lower substrate 1.
The related art device also includes an insulating layer 16. The insulating layer 16 includes a gate insulating layer formed between the gate line 11 and the data line on the lower substrate 1, and a passivation layer formed between the data line 12 and the pixel electrode 13 on the lower substrate 1.
Also, the above MVA mode LCD device uses the liquid crystal 3 having the negative dielectric anisotropy. A voltage is then applied to the pixel electrode 13 through the thin film transistor to align the liquid crystal 3. The alignment of liquid crystal will now be explained according to a white or black state.
The related art MVA mode LCD device is normally represented in a black mode. As shown in FIG. 2, during the voltage-off state, the MVA mode LCD device is in a black state. That is, the liquid crystal is aligned vertically due to the alignment layer 21 formed on the lower or upper substrate 1 or 2 and rubbed in a vertical direction, whereby the LCD device is in the black state.
As the voltage is applied to the MVA mode LCD device, as shown in FIG. 3, a vertical electric field is generated between the common electrode 7 of the upper substrate 2 and the pixel electrode 13 of the lower substrate 1. Thus, molecules of the liquid crystal 3 are tilted adjacently towards a horizontal surface. In this instance, the vertical electric field may be distorted due to the valley 15 and the transmitting part 14. That is, an electric field of equipotential is generated to be tilted relative to the valley 15 and the transmitting part 14. Then, the liquid crystal 3 is aligned in a vertical direction with respect to the equipotential line. At this time, the transmitting part 14 and the valley 15 function as a boundary between domains having the different alignment directions of liquid crystal.
In addition, form the valley 15 in the upper substrate 2, a mask is used for forming the color filter layer 6. The mask includes a semi-transmission part corresponding to the valley 15, and transmission and closed parts corresponding to the other portions except the valley 15. That is, a predetermined portion of the color filter layer 6 corresponding to the valley 15 is removed at a predetermined thickness, and the other portions of the color filter layer 6 corresponding to the pixel region are kept intact. Then, the color filter layer 6 corresponding to the other portions except the pixel region is completely removed.
For example, if the color filter layer 6 has the thickness of 1˜2 μm, the removed predetermined portion of the color filter layer 6 corresponding to the valley 15 is about half of the entire thickness thereof. At this time, the width of the valley 15 in the surface of the color filter layer 6 is about 7 μm.
The valley 15 has a slope angle of about 60° relative to the surface of the second substrate 2. As shown in FIG. 4, as some molecules of the liquid crystal 3 enter into the valley 15, the molecules inside the valley 15 may be aligned in the vertical direction (B) to the slope surface of the valley 15, or may be tilted in the direction of (A) or (C), according to the electric field applied between the common electrode 7 and the pixel electrode.
However, the related art multi-domain LCD device has the following disadvantages.
The vertical alignment mode LCD device using the valley is suitable for obtaining a rapid response time. To form the valley of the LCD device, it is necessary to provide the mask which includes the semi-transmission part as well as the transmission and closed parts. Thus, the process requires an additional mask including the semi-transmission part for the valley, thereby increasing the manufacturing cost, and lowering the yield due to the photo process after forming the valley. In addition, even though the semi-transmission part of the mask is used in the general exposure process, it is difficult to maintain a uniform width and depth of the valleys in each region.